Chemical substance concentrator and chemical substance detecting device

ABSTRACT

A chemical substance concentrator is configured to concentrate a chemical substance in a gaseous object. The chemical substance concentrator includes a channel in which a gaseous object flows, an adsorbent being conductive and configured to adsorb the chemical substance, and a pair of electrodes configured to cause a current to flow in the adsorbent.

TECHNICAL FIELD

The present invention relates to a technique for analyzing and detecting a chemical substance in a gas.

BACKGROUND ART

As a technique for analyzing a chemical substance in a gas, PTL 1 discloses a device for analyzing an organic substance in a gas inside electric power equipment. In this device, a gas passes through a pipe while a temperature of a trap is constant so that an organic substance in the gas is adsorbed on an adsorbent. Then, the trap is heated to introduce the adsorbed organic substance to a detector. PTL 2 discloses a device for trace level detection of an analyte using an adsorbent material capable of adsorbing an analyte and desorbing a concentrated analyte.

CITATION LIST Patent Literatures

PTL 1: Japanese Patent Laid-Open Publication No. 2001-296218

PTL 2: Japanese Patent Laid-Open Publication No. 2002-518668

SUMMARY

A chemical substance concentrator is configured to concentrate a chemical substance in a gaseous object. The chemical substance concentrator includes a channel in which the gaseous object flows, a conductive adsorbent that is disposed in the channel and is configured to adsorb the chemical substance, and a pair of electrodes configured to cause a current to flow in the adsorbent.

The chemical substance concentrator can desorb the adsorbed chemical substance with low power consumption.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a chemical substance concentrator according to an exemplary embodiment.

FIG. 2 is a schematic diagram of a detecting device including the chemical substance concentrator according to the embodiment.

FIG. 3A illustrates an arrangement of a conductive adsorbent in a channel of the chemical substance concentrator according to the embodiment.

FIG. 3B illustrates another arrangement of the conductive adsorbent in the channel of the chemical substance concentrator according to the embodiment.

FIG. 3C illustrates still another arrangement of the conductive adsorbent in the channel of the chemical substance concentrator according to the embodiment.

DETAIL DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 is a schematic diagram of chemical substance concentrator 1 of detecting device 100 according to an exemplary embodiment. In chemical substance concentrator 1 (hereinafter referred to as a concentrator), adsorbent 12 adsorbs a chemical substance in a gaseous object flowing into concentrator 1, concentrates the adsorbed chemical substance, then desorbs the chemical substance from the adsorbent by heating, and sends the chemical substance to detector 2 at a subsequent stage. The chemical substance may be volatile organic compounds, such as ketones, amines, alcohols, aromatic hydrocarbons, aldehydes, esters, organic acids, hydrogen sulfide, methyl mercaptan, and disulfide.

Concentrator 1 includes channel 11 in which a gaseous object flows, conductive adsorbent 12 disposed in channel 11, a pair of electrodes 13 a and 13 b configured to cause a current to flow in adsorbent 12, and cooling unit 14 configured to cool the gaseous object flowing in channel 11. Current supply unit 15 supplies current I to the pair of electrodes 13 a and 13 b. Controller 16 controls operations of cooling unit 14 and current supply unit 15. Adsorbent 12 is configured to adsorb a chemical substance contained in the gaseous object.

Concentrator 1 according to the embodiment includes conductive nanowires 12 a connected between electrodes 13 a and 13 b facing each other as adsorbent 12 for a chemical substance. That is, in a process of cooling by cooling unit 14, the chemical substance in the gaseous object is adsorbed on surfaces of nanowires 12 a, and is collected and concentrated. Then, current supply unit 15 causes a slight amount of current I to flow in nanowires 12 a through electrodes 13 a and 13 b so that nanowire 12 a generates heat (self-heating) by the Joule effect. A temperature rise due to the self-heating of nanowires 12 a causes the chemical substance adsorbed on the surface of nanowire 12 a to be desorbed and introduced to detector 2 at the subsequent stage. That is, conductive nanowires 12 a function also as a heating unit for heating the chemical substance.

This configuration and operation of concentrator 1 can send the concentrated chemical substance to detector 2 with low power consumption without using an external heater consuming a large amount of electric power.

In conventional configurations disclosed in PTLs 1 and 2 requires a heating unit, such as an external heater, in introducing an adsorbed chemical substance to a detector. If a chemical substance is desorbed without using a heater, the chemical substance is insufficiently desorbed. For this reason, the conventional detecting devices consume a large amount of electric power. Specifically, a heater used in the conventional technique needs about several tens to several hundreds of milliwatts of electric power. A technique for micro electro mechanical systems (MEMS) includes, e.g. a Pt-wire resistance heater requiring several milliwatts or more of power consumption.

As described above, a heater used in the conventional technique requires about several tens to several hundreds of milliwatts of electric power, whereas the technique according to this embodiment can desorb the chemical substance with electric power not larger than about 10 μW. In addition, the technique according to the embodiment needs no external heaters, hence reducing the size of detecting device 100 including the concentrator.

Here, when current I flows in a conductor, heat quantity Q generated by resistance R of the conductor is expressed as follows (Joule effect):

Q=R·I ² ·t

A relation between heat quantity Q and temperature change ΔT can be expressed with thermal capacity C of a conductor that is a product of a specific heat and a mass of the conductor:

Q=C·ΔT

Thermal capacity C depends on the mass (volume) of the conductor. Thus, a substance, such as nanowire 12 a, having a slight volume has small thermal capacity C. A very small amount of heat quantity Q generated when a current flows provides a large amount of temperature change ΔT.

In accordance with this embodiment, the reason for using nanowires 12 a as adsorbent 12 is that nanowires 12 a have a large specific surface area and a high concentration (adsorption) efficiency, and in addition, has small thermal capacity C providing a large temperature change with low power consumption. Another material having a large specific surface area may be a porous body. The porous body, however, has a larger volume than nanowires 12 a, and consumes larger electric power than nanowires 12 a due to self-heating by the Joule effect. Conductive adsorbent 12 according to this embodiment may not necessarily be implemented by nanowires 12 a, but by another structure, such as the porous body.

Conductive adsorbent 12, such as nanowires 12 a or the porous body, contains metal oxide, such as SnO₂, ZnO, In₂O₃, In_(2-x)Sn_(x)O₃ (where 0.1≦x≦0.2, for example), NiO, CuO, TiO₂, or SiO₂, metal, such as Al, Ag, Au, Pd, and Pt, and conductive material, such as carbon or silicon. As nanowires of carbon, carbon nanotubes may be used, for example. That is, a material of the adsorbent is made of a conductive material having a resistance enough to effectively exhibit self-heating due to the Joule effect.

The material of electrodes 13 a and 13 b according to this embodiment may be metal, such as gold, platinum, silver, copper, or aluminium, conductive oxide, such as indium tin oxide (ITO) or Al-doped zinc oxide (AZO), or conductive polymers. Electrodes 13 a and 13 b may have uneven surfaces. That is, electrodes 13 a and 13 b have shapes conforming with unevenness of the surface of nanowires 12 a or the porous body. Apart of adsorbent 12 may be embedded in electrodes 13 a and 13 b. For example, respective ends of nanowires 12 a may be embedded in electrodes 13 a and 13 b. A part of the porous body may be embedded in electrodes 13 a and 13 b. Chemical substance concentrator 1 can thereby connect electrically between adsorbent 12 and each of electrode 13 a and 13 b.

FIG. 2 is a schematic diagram of chemical substance detecting device 100 including concentrator 1 according to the embodiment. In the configuration illustrated in FIG. 2, frame 18 made of, e.g. polydimethylsiloxane (PDMS), epoxy resin, polyvinylidene chloride resin, or glass is provided on surface 17 a of substrate 17, such as a silicon substrate, a glass epoxy substrate, or a ceramics substrate. Channels 11 a, 11 b, and 11 c are formed in frame 18 as microchannels in which a gaseous object flows. Channels 11 a, 11 b, and 11 c extend to detector 2 from concentrator 1 into which the gaseous object flows. Although three channels 11 a, 11 b, and 11 c are shown in FIG. 2, the number of channels is not limited to three.

In concentrator 1, each pair of electrodes 13 a and 13 b are disposed on top and bottom of respective one of channels 11 a, 11 b, and 11 c. Nanowires 12 a are disposed between electrodes 13 a and 13 b. Cooling device 14 a, such as a Peltier device, is provided on surface 17 b of substrate 17 opposite to surface 17 a of substrate 17. Cooling device 14 a functions as cooling unit 14 configured to cool a gaseous object flowing in channels 11 a, 11 b, and 11 c. In detector 2, sensors 21 for detecting a particular chemical substance are arranged in channels 11 a, 11 b, and 11 c. In FIG. 2, wires for allowing current to flow in electrodes 13 a and 13 b, wires for supplying electric power to sensors 21, and wires for outputting detection signals of sensors 21 are not shown.

The configuration illustrated in FIG. 2 of concentrator 1 adsorbs and concentrates the chemical substance contained in the gaseous object flowing in channels 11 a, 11 b, and 11 c, and detector 2 detects the concentrated chemical substance. That is, in a process of cooling by cooling device 14 a, the chemical substance in the gaseous object is adsorbed on the surfaces of nanowires 12 a, and is concentrated and collected. Then, a current flows in nanowires 12 a through electrodes 13 a and 13 b, thereby causing self-heating of nanowire 12 a. A temperature rise due to the self-heating causes the chemical substance adsorbed on the surface of nanowire 12 a to be desorbed, introduced to detector 2, and detected by sensors 21.

In the configuration illustrated in FIG. 2, electrodes 13 a and 13 b are disposed on top and bottom of each of channels 11 a, 11 b, and 11 c. However, the positions of electrodes 13 a and 13 b are not limited to this configuration, and electrodes 13 a and 13 b may be disposed at any locations as long as current can flow in nanowire 12 a.

In the configuration illustrated in FIG. 2, cooling device 14 a is disposed on surface 17 b of substrate 17. The position of cooling device 14 a is not limited to this configuration, and may be at any location as long as cooling device 14 a can cool a gaseous object. For example, cooling device 14 a may be disposed on frame 18 or on electrode 13 a or 13 b. In the case where cooling device 14 a is disposed on electrode 13 a or 13 b, an insulator may be disposed between cooling device 14 a and electrode 13 a or 13 b.

FIGS. 3A to 3C illustrate arrangements of conductive adsorbent 12, such as nanowires 12 a. In FIG. 3A, adsorbent 12 includes plural groups 31A to 31C that are disposed separately from one another. Similarly to the configuration illustrated in FIG. 2, groups 31A, 31B, and 31C are disposed in channels 11 a, 11 b, and 11 c, respectively. In FIG. 3B, adsorbent 12 includes plural groups 32A to 32D that are disposed separately from one another, and groups 32A, 32B, 32C, and 32D are aligned perpendicularly to a direction in which the gaseous object flows in channel 11. In FIG. 3C, adsorbent 12 includes plural groups 33A to 33D that are disposed separately from one another, and groups 33A, 33B, 33C, and 33D are aligned in a direction in which the gaseous object flows in channel 11.

As illustrated in FIG. 2 and FIGS. 3A to 3C, conductive adsorbent 12 (nanowires 12 a) includes plural groups separate from one another. In this case, the groups constituting conductive adsorbent 12 may be made of different materials or may be provided with different surface modifications (coatings). This configuration enables gas molecules to be selectively adsorbed and concentrated. For example, since gas molecules are easily adsorbed on the surface having the same polarity as the gas molecules, if plural nanowires 12 a (adsorbents 12) having surfaces having different polarities are prepared as the conductive adsorbents, adsorption of polar molecules is dominant over adsorption of non-polar molecules on conductive adsorbent 12 having a surface having high polarity, and adsorption of non-polar molecules is dominant over adsorption of polar molecules on the conductive adsorbent having a surface having no polarity. That is, the groups of conductive adsorbent 12 preferably include groups made of different materials. Alternatively, the groups of adsorbent 12 preferably include groups provided with different surface modifications.

In the case where conductive adsorbent 12 includes plural groups, current supply unit 15 for supplying a current to conductive adsorbent 12 is preferably configured to selectively supply currents to plural pairs of electrodes provided on the groups. In this manner, the timing of desorbing the chemical substance adsorbed on each group of conductive adsorbent 12 can be controlled for each group of conductive adsorbent 12. For example, chemical substances adsorbed on the groups of conductive adsorbent 12 can be sent in a predetermined order to a detector at a subsequent stage. Thus, in the case where the chemical substance adsorbed on each group of conductive adsorbent 12 is specified, a precise analyzer is not needed as the detector at a subsequent stage. As a result, the size of detecting device 100 can be reduced.

In detecting device 100 according to the embodiment, since a current flows from current supply unit 15 to conductive adsorbent 12, a resistance of conductive adsorbent 12 can be monitored. On the other hand, the resistance of conductive adsorbent 12 changes depending on adsorption of the chemical substance. For example, in the case where conductive adsorbent 12 is made of metal oxide, the amount of oxygen in the surface of conductive adsorbent 12 changes depending on adsorption of the chemical substance to change the resistance. Even in the case where conductive adsorbent 12 is made of silicon, as long as adsorbed molecules have polarity, the resistance changes in accordance with the amount of adsorption of the molecules. Thus, as illustrated in FIG. 1, concentrator 1 according to the embodiment may include adsorption-amount estimation unit 115 that estimates the amount of the chemical substance adsorbed on conductive adsorbent 12 based on the change of the resistance of conductive adsorbent 12.

Adsorption-amount estimation unit 115 previously stores a relation between the amount of adsorption of a chemical substance and a change of a resistance of nanowires 12 a of adsorbent 12. Adsorption-amount estimation unit 115 detects the change of the resistance value based on the amount of the current flowing in adsorbent 12. Based on the detected change, the amount of a chemical substance adsorbed on adsorbent 12 is estimated with reference to the previously stored relation between the resistance and the amount of adsorption of the chemical substance. The presence of adsorption-amount estimation unit 115 as described above enables controller 16 to more accurately control a timing when an adsorbed chemical substance is desorbed.

As described above, chemical substance concentrator 1 is configured to concentrate a chemical substance in a gaseous object. Chemical substance concentrator 1 includes channel 11 (11 a, 11 b, 11 c) in which the gaseous object flows, conductive adsorbent 12 that is disposed in channel 11 (11 a, 11 b, 11 c) and adsorbs the chemical substance, the pair of electrodes 13 a and 13 b for causing current to flow in adsorbent 12, and cooling unit 14 for cooling the gaseous object flowing in channel 11 (11 a, 11 b, 11 c).

In this aspect, conductive adsorbent 12 that adsorbs the chemical substance is disposed in channel 11 in which the gaseous object flows. The pair of electrodes 13 a and 13 b configured to cause a current to flow in adsorbent 12. In a process of cooling by cooling unit 14, the chemical substance in the gaseous object is adsorbed on the surface of adsorbent 12, and is concentrated and collected. Then, a current flows in adsorbent 12 through electrodes 13 a and 13 b so that adsorbent 12 can generate heat due to the Joule effect. A temperature rise due to this heat causes the chemical substance adsorbed on the surface of adsorbent 12 to be desorbed. Chemical substance concentrator 1 can thus send the concentrated chemical substance to detector 2 with low power consumption without using an external heater consuming a large amount of electric power. In addition, since no external heaters are needed, the size of detecting device 100 can be reduced.

In the case where a sufficient amount of the chemical substance is adsorbed on adsorbent 12 without cooling the gaseous object, chemical substance concentrator 1 may not necessarily include cooling unit 14.

Adsorbent 12 may be nanowires 12 a.

Nanowires 12 a can cause a large temperature change with low power consumption so that power consumption of chemical substance concentrator 1 can be further reduced.

Adsorbent 12 may be a porous body.

Adsorbent 12 may contain a metal oxide, a metal, carbon, or silicon.

Adsorbent 12 may include groups 31A to 31C that are disposed separately from one another.

Groups 31A to 31C of adsorbent 12 may include groups made of different materials or may be provided with different surface modifications.

In these aspects, groups 31A to 31C of adsorbent 12 can selectively concentrate different types of chemical substances.

Chemical substance concentrator 1 may further include current supply unit 15 configured to supply a current to the pair of electrodes 13 a and 13 b. The pair of electrodes 13 a and 13 b includes plural pairs of electrodes 13 a and 13 b each provided on respective one of groups 31A to 31C of adsorbent 12. Current supply unit 15 is configured to selectively supply currents to the pairs of electrodes 13 a and 13 b.

In this aspect, the adsorbed and concentrated chemical substance can be selectively desorbed from adsorbent 12.

Chemical substance concentrator 1 may include substrate 17 having surfaces 17 a and surface 17 b opposite to surface 17 a, and frame 18 provided on surface 17 a of substrate 17. Frame 18 includes channel 11 (11 a, 11 b, 11 c) therein. Cooling unit 14 is cooling device 14 a disposed on surface 17 b of substrate 17.

Adsorption-amount estimation unit 115 detects a change of a resistance of adsorbent 12 based on an amount of a current flowing in adsorbent 12, and estimates, based on the detected change, an amount of the chemical substance adsorbed on adsorbent 12.

In this aspect, timing when the adsorbed and concentrated chemical substance is desorbed can be more accurately controlled.

Detecting device 100 includes chemical substance concentrator 1 and detector 2 into which the chemical substance concentrated by chemical substance concentrator 1 is introduced. Detector 2 includes a detection element, such as a semiconductor sensor, an electrochemical sensor, an elastic wave sensor, or a field effect transistor sensor. The detection element is not limited to these sensors. Detector 2 can employ an optimum detection element for detecting the chemical substance concentrated by chemical substance concentrator 1.

The above configuration provides chemical substance detecting device 100 (100A) with low power consumption and a small size.

INDUSTRIAL APPLICABILITY

A chemical substance concentrator according to the present invention can detect a chemical substance in a gaseous object with a small-size detecting device with low power consumption, and thus, is useful for, e.g. an ultrasmall chemical sensor capable of detecting a volatile organic compound in user's environments.

REFERENCE MARKS IN THE DRAWINGS

-   1 chemical substance concentrator -   2 detector -   11, 11 a, 11 b, 11 c channels -   12 adsorbent -   12 a nanowire -   13 a, 13 b electrodes -   14 cooling unit -   14 a cooling device -   15 current supply unit -   16 controller -   17 substrate -   18 frame -   31A-31C, 32A-32D, 33A-33D adsorbent groups -   100 detecting device -   115 adsorption-amount estimation unit 

1. A chemical substance concentrator configured to concentrate a chemical substance in a gaseous object, the chemical substance concentrator comprising: a channel in which the gaseous object flows; an adsorbent disposed in the channel, the adsorbent being conductive and configured to adsorb the chemical substance; and a pair of electrodes configured to cause a current to flow in the adsorbent.
 2. The chemical substance concentrator of claim 1, wherein the adsorbent comprises nanowires.
 3. The chemical substance concentrator of claim 1, wherein the adsorbent comprises a porous body.
 4. The chemical substance concentrator of claim 1, wherein the adsorbent contains metal oxide, metal, carbon, or silicon.
 5. The chemical substance concentrator of claim 1, wherein the adsorbent comprises a plurality of groups disposed separately from one another.
 6. The chemical substance concentrator of claim 5, wherein the plurality of groups of the adsorbent comprises groups made of different materials or groups having different surface modifications thereon.
 7. The chemical substance concentrator of claim 5, further comprising a current supply unit configured to supply a current to the pair of electrodes, wherein the pair of electrodes comprises a plurality of pairs of electrodes, each of the pairs of electrodes being provided on respective one of the plurality of groups of the adsorbent, and wherein the current supply unit is configured to supply the current selectively to the plurality of pairs of electrodes.
 8. The chemical substance concentrator of claim 1, further comprising a cooling unit configured to cool the gaseous object flowing in the channel.
 9. The chemical substance concentrator of claim 8, further comprising: a substrate having a first surface and a second surface opposite to the first surface; and a frame disposed on the first surface of the substrate, the frame having the channel therein, wherein the cooling unit is a cooling device disposed on the second surface of the substrate.
 10. The chemical substance concentrator of claim 1, further comprising an adsorption-amount estimation unit configured to detect a change of a resistance of the adsorbent based on an amount of a current flowing in the adsorbent as to estimates an amount of the chemical substance adsorbed on the adsorbent based on the change.
 11. A chemical substance detecting device comprising: the chemical substance concentrator of claim 1; and a detector to which the chemical substance concentrated by the chemical substance concentrator is introduced. 